[basic.align] Add \grammarterm for alignment-specifier (#8721)

Author: Andreas-Krug

source/basic.tex

@@ -3766,7 +3766,7 @@
 integer value representing the number of bytes between successive addresses
 at which a given object can be allocated. An object type imposes an alignment
 requirement on every object of that type; stricter alignment can be requested
-using the alignment specifier\iref{dcl.align}.
+using the \grammarterm{alignment-specifier}\iref{dcl.align}.
 Attempting to create an object\iref{intro.object} in storage that
 does not meet the alignment requirements of the object's type
 is undefined behavior.